1. Field of the Invention
This invention relates to a communication method, a transmitter, and a receiver, and more particularly, is suitably applied to a radio communication system such as a portable telephone system.
2. Description of the Related Art
An area of providing communication service is divided into cells having a predetermined size so that base stations are respectively set in the cells as a fixed radio station, and a portable telephone as a mobile radio station communicates by radio with a base station within the cell in which the portable telephone itself exists. In this case, various communication methods are considered as a communication method between the portable telephone and the base station, and a typical method is a time division multiple access (TDMA) method.
This TDMA method is such that a predetermined frequency channel (hereinafter, simply referred to as a channel) is classified in time with frames having a predetermined time width and moreover, the frames are respectively divided into time slots having a predetermined time width, and the channel is used at a timing of a time slot which is assigned to its own station to transmit a transmission signal. The method realizes a plurality of communication (so-called multiple communication) with the same channel to effectively use frequencies.
However, in a radio communication system using the TDMA system, for example, in the case where the same channel is assigned between adjacent cells and moreover, communication is performed by using the same time slot in terms of time, the same channel interference (that is, two electronic waves having the same frequency interfere with each other at a receiving point to cause interference with each other) may occur to cause communication trouble.
For example, as shown in FIG. 1, while a portable telephone 2A communicates by radio with a base station 3A using a predetermined channel in a cell 1A, when a portable telephone 2B communicates by radio with a base station 3B by using the same channel in an adjacent cell 1B, it sometimes happens that a transmission signal CB transmitted by the portable telephone 2B reaches the base station 3A. If the transmission signal CB, which has reached the base station 3A, overlaps in timing with a transmission signal CA transmitted from the portable telephone 2A to the base station 3A, it becomes an interference wave SI (so-called trouble wave) against the transmission signal CA and causes trouble to the communication between the portable telephone 2A and the base station 3A.
Here, a particular problem in the case of the TDMA method is, as shown in FIGS. 2A and 2B, a case in which the portable telephone 2A and the base station 3A communicate by using a time slot TS0 out of four time slots TS0 to TS3 and the portable telephone 2B and the base station 3B also communicate by using a time slot TS0 which completely overlaps in timing (that is, synchronizes) with the time slot TS0. In this case, each of the time slots are arranged in a regular manner, so that the time slots agree with each other not only at the first time slot TS0 but also at the time slots TS0 after that. In the case where such a situation is generated, the same channel interference occurs at all times to cause continuous trouble to the communication between the portable telephone 2A and the base station 3A, so that the communication quality may be continuously deteriorated and the communication may become impossible in the worst case.
In view of the foregoing, an object of this invention is to provide a communication method, a transmitter and a receiver which can avoid continuously suffering interference from another communication even when the same channel is used to perform the other communication based on the time division multiple access.
The foregoing object and other objects of the invention have been achieved by the provision of a transmitting method for transmitting a plurality of information in time sharing, wherein the plurality of information is arranged in a predetermined order, information different from the plurality of information is inserted at random between the plurality of information arranged in the predetermined order, and the plurality of information is transmitted to a predetermined transmission channel. Further, a receiving method for receiving information in time sharing receives a signal, demodulates a reception signal, deletes different information inserted at random on a transmitting side, from the demodulation output, and decodes desired information. Furthermore, a transmitter for transmitting a plurality of information in time sharing, comprises first means for arranging the plurality of information in a predetermined order, second means for inserting information different from the plurality of information, at random between the plurality of information arranged in the predetermined order, and transmitting means for transmitting the output to a predetermined transmission channel. Furthermore, a receiver for receiving information in time sharing, comprises receiving means for receiving a signal, demodulating means for demodulating a reception signal, deleting means for deleting different information inserted at random at a transmitting side, from the demodulation output, and decoding means for decoding desired information.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.